unit 5 forensics fiber student notes - weebly
TRANSCRIPT
![Page 1: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/1.jpg)
Fiber
Come in and get your notebooks out. We have notes today!
![Page 2: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/2.jpg)
• Defined as the smallest unit of a textile visible to the naked eye
• Used as supporting evidence to help place an individual at the crime scene
• 95% of fibers are lost within the first 24 hours, so fiber collection at the beginning of an investigation is critical
What is a FIBER?
![Page 3: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/3.jpg)
▪Are considered class evidence
▪Are common trace evidence at a
crime scene
▪Can be characterized based on
comparison of both physical and
chemical properties
▪Fabric is made of fibers. Fibers are
made of twisted threads.
FIBER
FABRIC?
![Page 4: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/4.jpg)
Fiber Transfer
• Direct transfer: fibers transferred directly from victim to suspect or suspect to victim
• Secondary transfer: a victim has fibers that were picked up and then transferred to the suspect
![Page 5: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/5.jpg)
When you analyze an unknown fiber, what do you look
for?
Ultimately, you want to know what kind of fiber it is!
Texture
Color
Origin
Crimp
New TermsCrimp: is the fiber straight or crimped (wavy)Pliability: is the fiber pliable (bends) or non-pliable (breaks)Resilience: is the fiber resilient (reshapes after being crumpled)
PliabilityResilience
Odor
![Page 6: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/6.jpg)
Fibers
Natural Fibers
Synthetic Fibers
*Animal*Plant
*Mineral
Naturally occurring materials Man-Made Materials
*Regenerated Fibers
*Synthetic Polymer Fibers
![Page 7: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/7.jpg)
Common Fiber Types
Synthetic▪Rayon
▪Nylon
▪Acetate
▪Acrylic
▪Spandex
▪Polyester
Natural▪Silk
▪Cotton
▪Wool
▪Mohair
▪Cashmere
Sometimes microscopic images are not enough to categorized a fiber. Other
tests should be preformed.
![Page 8: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/8.jpg)
Natural Fibers—Animals
• Fur—used to make coats and gloves
• Hair—wool (sheep), cashmere and mohair (goats), and angora (rabbits, camels, llamas, alpacas)
• Silk—from the cocoons of the silk caterpillar
All animal fibers are made up of protein.
![Page 9: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/9.jpg)
Natural Fibers—Plant
• Seeds—cotton is in the seedpod of cotton plants; easily woven and dyed so common in clothing
• Fruit—coir is made from the covering surrounding coconuts; used to make baskets
• Stem—flax (linen) and jute(twine)
• Leaf—manila and sisal; both used for twine
All plant fibers are made up of cellulose.
![Page 10: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/10.jpg)
Natural Fibers—Mineral
• Fiberglass—fiber form of glass that is weak and brittle; used as insulation
• Asbestos—very durable fibers used for pipe coverings, brake linings, ceiling tiles, and other uses
![Page 11: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/11.jpg)
Synthetic Fibers—Regenerated Fibers
• Cellulose is combined with chemicals such as acetate
• Rayon—imitates natural fibers and generally is smooth and silky in appearance
• Celanese—cellulose combined with acetate; used in carpets
• Capron—breathable, light weight material used in high performance clothing
![Page 12: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/12.jpg)
Synthetic Fibers—Synthetic Polymer Fibers
• Polyester—common synthetic fiber; represents a large group of fibers with a common chemical makeup
• Nylon—similar to polyester, but easily broken down by light and concentrated acid
• Acrylic—found in artificial wool or imitation fur; has a light, fluffy feel
• Olefins—used in high performance clothing such as thermal socks and carpets because they are quick drying and resist wear
![Page 13: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/13.jpg)
Filament Cross-Sections
Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross-section.
![Page 14: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/14.jpg)
• Fibers are woven into textiles(fabrics)
• Weaving consists of arranging lengthwise threads (the warp) side by side and close together
• Crosswise threads (the weft) are then woven back and forth in one of several different patterns
Textiles
![Page 15: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/15.jpg)
Weave Patterns
• Plain: alternating warp and weft threads; firm and wears well, snag resistant, tends to wrinkle
• Basket: alternating pattern of two weft crossing two warp threads; doesn’t wrinkle, not durable, shrinks when washed
• Satin: one weft crosses over three or more warp threads; not durable, snags, shiny surface, high light reflectance
![Page 16: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/16.jpg)
Weave Patterns (cont.)
• Twill: weft is woven over three or more warps and then under one; next row, the pattern is shifted over one to the left or right by one warp thread; strong, dense, compact, diagonal design
• Leno: uses two warp threads and a double weft thread; the two adjacent warp threads cross over each other; the weft travels left to right and is woven between the two warp threads; easily distorted with wear and washing, stretches in one direction only
![Page 17: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/17.jpg)
Collection of Fiber Evidence
▪Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged.
▪Make tape lifts of exposed skin areas of bodies and any inanimate objects
▪Removed fibers should be folded into a small sheet of paper and stored in a paper bag.
![Page 18: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/18.jpg)
Collection and Preservation
• Clothing should be packaged in paper bags
• Each article must be placed in separate bags to prevent contamination
• Must keep clothing from different people from coming into contact
• Carpets, rugs, and bedding should be folded to protect areas suspected of containing fibers
• Knife blades should be covered to protect adhering fiber
• If a body was wrapped in a carpet or blanket, tape lifts must be done on the body
• If individual fibers are found, they must be removed with clean forceps and placed in a small sheet of paper, must be folded and labeled and placed in another container
![Page 19: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/19.jpg)
Forensic Examination of Fibers
• Important evidence in incidents involving personal contact- homicide, assault, sexual
• Cross-transfers may occur between the clothing of a suspect and victim
• Hit-and-run victims can leave fibers, threads, or whole pieces of clothing on a vehicle
• Fibers can also become fixed in screens or glass broken during a breaking-and-entering attempt
![Page 20: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/20.jpg)
Analytical Techniques Used
• Two fibers may seem to be the same color, differences may exist in the dyes applied to them when made
• Most fibers are dyed with a mixture of colors to obtain a desired shade
• Can use a visible light microspectrophotometer to compare the colors of fibers
• A fiber as small as 1 mm long or less can be examined
![Page 21: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/21.jpg)
![Page 22: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/22.jpg)
Analytical Techniques Used
• A more detailed analysis of the fiber’s dye composition can be obtained by a chromatographic separation of dye
• Small strands of fibers are compared for dye content by extracting the dye off each fiber with a solvent and then spotting the dye solution onto a thin-layer chromatography plate
• The dye of the questioned and standard fibers are separated on the plate and compared for similarity
![Page 23: Unit 5 Forensics Fiber Student Notes - Weebly](https://reader031.vdocument.in/reader031/viewer/2022013005/61cd12b7d101467f7f7a1d5c/html5/thumbnails/23.jpg)
Others• When fibers are compared, they must be shown to
have the same chemical composition (belong to the same class)
• For example, the standard and questioned fabric both being nylon instead of one being nylon while the other is cotton
• Many manufactured fibers exhibit double refraction or birefringence which will make it look crystalline
• Polarized white light will split into two rays that are perpendicular to each other and produce interference colors, polarization